Protective control system



April 1943- s. E. KlNG PROTECTIVE CONTROL SYSTEM Filed Oct. 24. 194.0

, INVENTOR ,WITNESSESI Patented Apr. 6,1943 e I l l I UNITED STATESPATENT OFFICE PROTECTIVE CONTROL SYSTEM I George E, King, Wilkinsburg,Pa., assignor to Westinghouse Electric 8; Manufacturing Company, EastPittsburgh, Pa.., a corporation of Pennsylvania Application October 24,1940, Serial No. 362,584

6 Claims. (Cl. 171-119) My invention relates generally to controlsystime after the operator has terminated a welding tems, and it hasreference in particular to a ope tio Su aun t y c p generally, safety orprotective control system for use with an impedance which-may beconnected between alternating current arc welding apparatus. oneterminal of the welder and the source and Generally stated, it is anobject of my invena switch for completing a shunt circuit about the tionto provide in a simple and effective manner impedance underpredetermined conditions. A for reducing the normal open circuit voltageof time delay relay y be utilized Control the a transformer typealternating current arc Operation of the switch so as to maintain it inwelder to prevent the operator from receiving a the closed position fora predetermined time shock therefrom by accidental contact with a afterthe termination Ofa Welding Operation A welding electrode. relayresponsive to the closure of the welding More specifically, it is anobject of my invencircuit may be provided to eflfect operation of tionto provide a. safety or protective control unit the time delay relay soas o effect Operation of which may be connected between an alternatingthe switch to shunt the impedance d pply current are welder and a sourceof welding curnormal voltage to the prim y winding o the rent to eifecta reduction of the open circuit volt- Welding t a s o Whe t secondaryage of the welder to a safe value a predetermined W d ng circuit isclosed.

interval of time after the termination of a weld- F0 a m Completeunderstanding o e ing operation. nature and scope of my inventionreference may Another object of myinvention is to provide be had to thefollowing detailed description for controlling the secondary voltage ofa transwhich may be taken in connection with the aciormer typealternating current are welder by 0mpa y n d w in which;

means of a control unit which may be connected F gu 1 illustratesdiagrammatically a W in the primary circuit of the welder. ing systemembodying the principal features of A further object of my invention isto provide t invention; 1 l

a safety control system for automatically reduc- 2 i st t sdiagrammatically an p ing the arc circuit voltage of an arc welder to 9.tion of a different embodiment of the invention; safe value apredeterminedinterval of time after and the termination of a weldingoperation, without I -"3 l s es diagrammatically a further requiringreduced voltage taps on the are welder. embodiment of the inventionapplied to a welding Yet another object of my invention is to prosystemutilizing a transformer type of alternatvide for normally reducing thevoltage applied to in current are welder.

the primary winding of a transformer type alter- Referring to Fig. 1,the reference numeral l0 nating current are welder, applying the fullvoltmay denote, generally, an alternating current are age thereto assoon as the welding circuit is comwelding system utilizing an arc welderl2 of the pleted. and reducing the voltage applied thereto transformertype having a seconda y Winding N a predetermined interval of time afterinterrupconnected to a welding circuit including the work tion of thewelding circuit. 1 I4 upon which a welding operation'is to be per- Stillanother object of my invention is to proformed and an electrode IS. Theprimary ndvide for automatically connecting an impedance g. '5 maybe o nc d to any suitable source in series circuit relation with the primarywindof alternating current power. ing of a transformer type alternatingcurrent In order to protect a weldi p r r from are welder so as toreduce the open circuit secshocks when changing or ac d y Coming ondaryvoltage of the welder to a safe value a into Contact with the electrodeI 5 while he is predetermined interval of time after the secondgroundedor elec ric lly connected to the work ary circuit is opened. l4,suitable means such as the safety or protec- Other objects will in partbe obvious, and will tive control unit l8 may be provided, being for inpart appear hereinafter, example connected between the primary windingIn accordance with my invention, a simple and I6 and the conductors 19,which are connected effective safety or protcctivecontrol unit may besoto a suitable source of alternating current. provided for connectionbetween the primary The control unit l8 may be provided with linewinding of a t 'a e ypo alternating curterminals 20 and 2i to which theconductors i9 rent arc welder and a source of alternating curmay beconnected, and load terminals 22 and rent to reduce the open circuitsecondary voltage which may be connected by means'of conductors of thewelder to a safe'value a predetermined 24 and 25, respectively, to thepposite terminals of the primary winding 5. For the purpose of normallyreducing the open circuit voltage of the secondary winding 16 to a safevalue when the operator is not welding, suitable means such as theimpedance 26 may be connected between the terminals 20 and 22 to reducethe voltage across the primary winding [6 under no load conditions tosuch a value that the voltage across the secondary winding [3 of thewelder is reduced to a safe value, for example, about 30 volts, insteadof the normal open circuit voltage which may be from 70 to 85 volts. Aswitch 21 having an operating winding 28 may be provided for controllingthe connections of the impedance 26 by completing a shunt circuit aboutthe impedance through contact members 210 to apply the full voltage ofthe source to the primary winding I6 under predetermined conditions.

In order to control the energization of the operating winding 23 so asto enable the operator to change or renew the electrode l8 safely,suitable means may be provided to effect operation of the switch 21 toshunt the impedance 26 whenever the welding circuit is closed, andmaintain the switch in the closed position for a predetermined intervalafter the welding circuit is opened, such as, for example, the timedelay relay 30.

The time delay relay 30 may be provided with an armature 3| actuated byan operating winding 32 which may be energized from a. suitable sourceof direct current voltage such as the rectifier bridge circuit 33,connected to the secondary winding 34 .of a control transformer 35. Therelay 30 may further be provided with suitable means to maintain it inthe operative position for a predetermined interval of time after itsoperating winding 32 is deenergized. For example, a short-circuiteddamper winding 3 may be positioned about the armature 3| to prevent thesudden collapse of the magnetic flux therein and thus delay the returnof the armature 3| to the deenergized position when the operatingwinding 32 is deenergized. Suitable adlusting means such as, forexample, the adiustable spring 31 may be provided for adjusting theduration of the delay.

With a view to controlling th energization of the operating winding 32,suitable control means responsive to the closure of the" welding circuitmay be provided, such as, for example, the current responsive relay 39for controlling the connection of the primary winding 33 of the controltransformer 35 to the source. The relay 3! may be provided with contactmembers 33a and an operating winding 40 which may be energized from thesecondary winding ll of a current transformer 42, the primary winding ofwhich may be connected in series circuit relation with the impedance 2B,

In order to permit the current responsive relay 39 to respond todifferences in the relatively small values of the primary current of thetransformer welder l2 while the impedance 26 is connected in seriescircuit relation therewith, and not be damaged by the relatively heavycurrent flowing in the primary circuit after the impedance 26 is shuntedout of the primary circuit, suitable means may be provided for limitingthe amount of current in the operating winding 40 of thecurrent-responsive relay 39. For example, a control resistor 43 may beconnected in shunt circuit relation with the operating winding 40 of thecurrent responsive relay 39 through contact members 30a of the timedelay relay, so

as to by-pass the operating winding 40 under load conditions.

When the primary winding ii of the welding transformer I2 is connectedthrough the control unit I8 to the conductors l9, and the weldingcircuit connected to secondary winding I3 is open, a. relatively smallmagnetizing current flows through the impedace 2i and the primarywinding IS. The impedance 28 may be of such a value that the voltageacross the primary winding is sufficiently reduced to produce an opencircuit voltage across the secondary winding l8 between the electrode 15and work ll of, for example, about 30 volts, which may be considered asafe value. The current flowing through the primary winding I! underthese conditions is insufficient to operate the current responsive relay3!.

of alternating current. The operating winding 32 of the time delay relay30 is energized, and the armature ll operates, closing contact members30a and 30b, thus connecting the control resistor I! in parallel withthe operating winding 40 of the current responsive relay 3! andconnecting the operating winding 28 of the switch 21 to the source. Theswitch 21 operates, closing contact members 210 and completing a shuntcircuit about the impedance 26. The full voltage of the alternatingcurrent source is then applied across the primary winding ii of thewelder l2 so that th normal welding voltage may be obtained between theelectrode l5 and the work II for periorming the desired weldingoperation.

If the welding circuit is interrupted momentarily, the currentresponsive relay Il may m turn momentarily to the deener'gized positionbecause of th reduction in the current flowing, through the primarywinding ll of the welder.-

but the time delay relay ll remains in the energiud position for apredetermined interval of time. The full open circuit voltage istherefore retainedbetweentheelectrode ll and the work ll for apredetermined time after the welding circuit is interrupted, in order tofacilitate recommencement of the welding operation. Should theoperatorin'terrupt the welding circuit for greater than thepredetcrminedinterval of time. which may, for example, be approximately 2 seconds,the time delay relay 3| returns to the deenergized position. Contactmembers 30b open, interrupting the energizing circuit for the operatingwinding 28 of the switch 21, so that the switch opens the shunt circuitand inserts the impedance 2' in the primary circuit 01 the transformer.welder l2, reducing the open circuit secondary voltage thereof to a safevalue.

Referring to Fig. 2, it may be seen that the control unit Ila isgenerally similar to the control unit ll of Fig. 1, except that theshunt circuit about the impedance 2' may be initially completed bycompleting an energizing circuit for the operating winding 20 of theswitch '11 through the contact members I: of a relay such as the voltagerelay 4. The operating winding 45 of the voltage relay 44 may beconnected in parallel circuit relation with the impedance 2i, and may beso designed that the voltage across the impedance 26 when the weldrelay,while the voltage thereacross which but the switch.-,2l

the becomes practically equal to the voltage of the source when thwelding circuit is closed, is sufficient.

In order to maintain the switch -21 in the closed position during awelding operation when the voltage across the impedance 28 is reduced tosubstantially zero, the primary winding ll of the control transformer 35may be initially connected. to the source of alternating current throughcontact members 44a of the voltage relay so as 'to'eii'ect operation ofthe time delay relay 30, as soon as the voltage relay 44 operates. Sincethe time delay relay 30 remains in the energized position for apredetermined interval of time after its operating winding 32 is ingcircuit is open, is insufilcient tooperate deenergized, the time delayrelay 30 maintains the energizing'circuit for the operating winding lloi the switch Zlfor a definite period after the switch I! closes and thevoltage relay 44 is deenergized thereby. Thereafter, the 'energizatlonoi theoperating winding of the time delay relay 30 may be maintainedduring a welding v operation byssuitable j respons'ive relay 145, whichmay beprovided with meanspsuch as the current foperating winding 41;connected v to the secondary winding 4| of the current transformer 42soas .to beresponsive to anormal value of priwelding operation.

mary cur'rentduring .a

When the operator brings the electrode it into,

short-circuiting the contact with ,t'he 'work i4,

transformer welder secondary winding ll of the l2,;th e voltage dropacross the primary' winding it is greatlyjq reduced, andxfthecurrenttherethrough increased, so that thevoltage drop across the impedance. 28 increases substantially. The increased voltag'e ei'fects operationoithe voltage v relay 44', wh ichsimultaneously connects the pri- -maryWinding'ilof the,.contro1 transformer, 36

. and the operating winding 28 of the switch 27 to the sourceofalternating current through the f contact members'44a iand 44b,respectively. The

time delay relay 3c operates, and the switch 21 closes, providing ashunt circuit about the impedance 26. I

The voltage relay-44.'is, therefore, 'deenergized,

position, since the operating winding 24 is connected to the alternatingcurrentsource through 30. When the current in the primary winding l6reaches a, predeterminedavalue, the current responsiverelay operates,connecting the primary winding a of the control transformer 35 to thealternating current source through contact members 45a to ei'i'e'ct.energization of the operatingwinding "got the time delay relay 3|!during the continuance of the welding operation. 1 Referring to Figj3,it will be seen that the protective control unit ilb thereof isgenerally similar to thevcontrol units Iii and Ila of Figs. 1 and 2,respectively, except that the current respon-' sive relay 48 of Fig. 3is provided with an operconnected to the secondary ating winding 49'transformer the winding 50=oia current primary winding 52 of whichisconnected in. 1 series circuit relation with provided with a tap theimpedance 26 and 53 adjacent one end. When is open, a relatively smallflows through the entire the transformer welder H,

the welding circuit magnetizing current primary winding I6 of which isinsufficient to effect operation of the current responsive relay 48.circuit is closed, the current in When the welding the primarywindismaintained in the closed impedance 26 and ing 52 of the currenttransformer 5|, the ratio ing l6 increases suificiently to effectoperation of the current responsive relay 48 which, as hereinbeforedescribed in connection with the relay 39 oi Fig. 1, completes anenergizing circuit for the operating winding 32 of the time delay relayfull voltage to the primary winding l6, so as to limit the current areasonable value under welding conditions and not overload the operatingwinding 48.

When the welding circuit is opened, the cur? rent responsiveinterruption of the welding circuit.

From the above description and the accom- V panying drawing it will beapparent that I have the contact members 30b of the time delay relaywelder or manufactured as a separate and disdrawing be considered asillustrative and not in a limiting sense.

I claim as my invention:

in the secondary winding tofor limiting the current through theoperating winding of the control relay.

2. A protective control system for an alternating current transformercomprising, an impedance for reducing the voltage applied to the primarywinding, switch means operable to shunt said impedance, a time delayrelay energizable to effect operation of the switch means for apredetermined time after the time delay relay is deenergized, a controlrelay controlling the energization of the time delay relay, means forenergizing the control relay to effect operation of said relay inresponse to a predetermined value of current supplied to thetransformer, and means for limiting the energization of the controlrelay when the current supplied to the transformer reaches thepredetermined value.

3. The combination with a transformer having a primary winding connectedto a source of alternating current and a secondary winding, of animpedance connected in series circuit relation with the primary windingof the transformer, a current transformerhaving a primary winding with atap connected in series circuit relation with the impedance and asecondary winding, means including a control switch and circuit meansconnected to the tap for providing a shunt circuit across the impedanceand a portion of the current transformer primary winding, a currentresponsive relay energized from the secondary winding of the currenttransformer, and a time delay relay operable for a predetermined timeafter deenergization to effect operation of. the control switchenergized in response to operation of the current responsive relay.

4. A safety control system for alternating cur rent transformer type arcwelders comprising, an impedance for connection to one terminal of theprimary winding of the welder, a current transformer having a primarywinding connected in series circuit relation with the impedance and asecondary winding, switch means operable to shunt the impedance, timedelay means operable for a predetermined time after deenergized toeffect operation of the switch means, a control relay energized from thesecondary winding of the current transformer for controlling theenergization of the time delay relay in accordance with predeterminedcurrent values in the primary winding of the current transformer, andmeans including a control resistor controlled by the time delay relay tolimit the energization of the control relay.

5. A voltage reducing system for a load circuit adapted to be connectedto a source of alternating current comprising, an impedance connected inseries circuit relation with the load circuit under light loadconditions, impedance means connected in series circuit relation withthe said impedance, control means operable in shunt the impedance and aportion of the impedance means, time delay means operable to effectsubstantially immediate operation of the control means, and meansenergized from the impedance device to effect operation of the timedelay means in response to increase of the load above a predeterminedvalue.

6. A protective system for a transformer having a primary winding forconnection to an alternating current source and a secondary windingcomprising, an impedance connected in series circuit relation with theprimary winding, a current transformer having a secondary winding and aprimary winding with a tap connected in series circuit relation with theimpedance. switch means connected between the tap and one end of theprimary winding, time delay means operable to control the switch means,and means energized from the secondary winding of the currenttransformer to control the operation of the time delay means.

GEORGE E. KING.

